Field of the Invention
The present invention relates to a four-primary-color organic light emitting display and a driving method thereof.
Discussion of the Related Art
Flat panel displays (FPD) are used in various electronic products, including cell phones, tablet PCs, laptops, etc.
An organic light emitting display, which is a type of flat panel display, is a self-luminous device that causes an organic light emitting layer to emit light via the recombination of electrons and holes. The organic light emitting display is regarded as the next-generation display owing to its high luminance, low operating voltage, and ultra-thin profile. Each individual pixel of the organic light emitting display comprises an organic light emitting diode (hereinafter, OLED), which is a light emitting element consisting of an anode and a cathode and an organic light emitting layer formed between the cathode and anode, and a pixel circuit for independently driving the OLED. The pixel circuit mainly comprises a switching thin film transistor (hereinafter, switching TFT), a storage capacitor, and a driving element (driving TFT). The switching TFT charges the capacitor with a data voltage in response to a scan signal, and the driving TFT adjusts the amount of light emitted by the OLED by controlling the amount of current supplied to the OLED based on the amount of voltage stored in the capacitor. The amount of light emitted by the OLED is proportional to the current supplied from the driving TFT.
An OLED generally displays various colors by mixing three primary colors, including R (red), G (green), and B (blue). Recently, OLEDs display four primary colors including R (red), G (green), B (blue), and W (white).
A four-primary-color organic light emitting display comprises pixels comprising R OLEDs that emit R, pixels comprising G OLEDs that emit G, pixels comprising B OLEDs that emit B, and pixels comprising W OLEDs that emit W. The R OLED, G OLED, B OLED, and W OLED differ in their physical properties such as luminous efficiency. Luminous efficiency is defined as the ratio of the amount of light emission to driving current. Accordingly, if the data voltage applied to the pixels is controlled for each color, it becomes easier to correct white color coordinates. To this end, the four-primary-color display converts input digital video data into an analog data voltage by using four digital-to-analog converters (hereinafter, DAC) corresponding to the four colors.
That is, for the four-primary color organic light emitting display, the data voltage Vdata for each gray level depending on the OLED characteristics varies with color, as shown in FIG. 1. Also, as shown in FIG. 2, assuming that the maximum grayscale value is 255, the maximum grayscale voltage for driving an OLED varies with color.
In such an individual gamma-type four-primary-color organic light emitting display, it is necessary for a data drive circuit to incorporate four DACs corresponding to the respective colors. This increases the chip size and manufacturing costs of integrated circuits.